P0304 Misfire Code/Cant Clear it. HELP!

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JMac101

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Hey guys I have posted a few threads on this site and through trial and error I have gotten great advice, but nothing has fixed the problem yet. About 6 months ago my check engine light came on. I scanned the codes and got a P0304 Misfire Cylinder #4 Code. I since then have changed many parts and attempted to clear the MIL and Code but it has returned. I have gone over kill with the amount of parts I changed.
The parts I have already changed are: Oil & Filter, Spark plugs, Wires, Coil Pack, Valve cover gasket & spark plug tube seals, Fuel Injectors, Fuel Rail, Fuel Rail Wiring harness(injector power), MAP Sensor for intake Manifold, throttle position sensor, EGR & EGR diaphram for vaccuum & more that I cannot remember off of the top of my head.
I still have the check engine MIL light lit up with the code P0304. At Idle it blinks, While driving it is steady unless I am driving at high speeds. I feel like I have more power, I do not have the stumble when I accelerate after changing the EGR. However, after driving I do smell a fuel odor from the motor and I do have white smoke from the exhaust upon startup for about 45 Seconds to a minute then blows normal.
People were telling me, Could be the cars computer or even a injector driver? Anyone with any advice or anyone that has the same problem please help me out. I have state inspection coming up soon and I cant pass with this light. I put so much time, blood, sweat and tears into this car because it belonged to my father in law that passed away and he left it to me, so it is kind of a priority to keep it running. If I have to go to a mechanic I will I just dont want to bring it if it is a simple fix.
Thanks Guys.
 
Plus I forgot to mention that I had extremely rough idle before changing the EGR. Also the mechanic at a local shopped checked it out and said my cat was decent and not clogged up.
 
At face value, sounds to me like that hole has low compression.

I'd want to see what a cylinder leakdown test shows. I'd bet you have a burned valve.

Of course, depending on the type of car, which you neglected to share with us, it could be other things....
 
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Could it be the lower intake manifold gasket? where the intake manifold bolts onto the bottom of the crankcase below the spark plugs?
 
Could be, I guess.

If the intake leaks on the BOTTOM cylinder #4's port only, and this is a GM V6 (is it???), then that cylinder could have a vacuum leak that you can't hear and is hard to catch until its too late. Too late being burned up valves on that cylinder due to running lean, meaning the head has to come off to fix the valves...
 
Hmm, on a 2.4, that had a dry intake manifold....if you can get in there, get a propane torch, and with it UNLIT but with the gas turned on, point it all around the point where the intake bolts to the head for that cylinder while the engine is idling, and again at 1500 rpm or so. If the engine suddenly sounds/acts/generally runs different when you introduce the propane, you found your intake/vacuum leak.

*Don't be pouring tons of unburnt propane in there for 10 minutes at a time or you might blow yourself up.

You could also substitute a product like aeresol carburator cleaner, or even WD40 for this, and just hose down that one port for #4 with the engine running. The engine should NEVER be able to tell you are spraying anything on it's outside like that, and if it does, it has a leak.
 
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As you may know, this code is for a cylinder misfire. On my windstar, it was caused by the plugging-up of the exhaust gas recirculation intake ports. The shop wanted $500 to fix it. I did it myself in about 4 hours (I work slow) and a $5 can of carburetor cleaner. If it is the same thing design as the ford, you take the top half of the intake manifold off the engine and clean out the little intake ports for each cylinder. With the ford, you do not have to deal with the gasket between the lower half and the block. What happened was that most of the ports were plugged and all the exhaust gas was going into one cylinder, causing a misfire. The smoothness at idle was amazing after I did this.

If not this, something is causing a cylinder misfire.
 
Burt - Your Saying remove the top half of the intake manifold and find the EGR ports? I know your saying to clean the intake ports like the walls in the intake and everything, but where are the EGR ports? If I disconnect my intake manifold top half the bottom will still be bolted in and all that is exposed is the fuel injectors.
 
Give me a few minutes and I think I maybe able to find a link with photos from a guy that did the same thing.
 
http://rides.webshots.com/photo/1201999780011220610BGkBnV

The link above shows the intake port with the upper half of the manifold removed. Note that in the right side of the hole on the right, there is a little donut looking thingy. This is the EGR port that I unplugged. The ports furthest from the source of the EG were the worse I believe, leaving all the gases to go into the nearest ones.

The link below shows more of the before and after steps:

http://rides.webshots.com/album/201931518cScpNK

Like I say, your engine may be of a different design, but my guess is your intake system is partially carboned up. i had carbon not only on these ports, but interior surfaces of the intake manifold.

Good Luck
 
You didn't mention changing plugs. If you needed to R&R VC plug well seals then you must of had a problem with miss fire before. If you just changed wires and didn't clean the carbon tracks off the upper porcelin on the plugs there is a good chance the arcing in the plug boot has re-occured. the wires connot be cleaned if you have carbon tracks running down the boot and need to be replaced again even if thay are new. The carbon will tatoo the rubber or silicone boot.
 
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